1. Field of the Invention
Embodiments of the present invention relate to a technology of radiating a plurality of orthogonal frequency division multiplexing (OFDM) based split band penetration signals toward a target object, and quickly obtaining a wideband response signal using a plurality of signals reflected from the target object.
2. Description of the Related Art
A ground penetrating radar apparatus may perform a technology of projecting a radio frequency (RF) penetration signal onto a target object, receiving a signal reflected from the target object, and thereby sensing an inside state of the target object as one of nondestructive inspection methods.
The conventional ground penetration radar apparatus may obtain a reflected signal using, for example, an impulse method and a step frequency method.
Here, the impulse method refers to a method of employing, as a projection signal, a signal having great energy during a relatively short period of time, that is, an impulse signal. An impulse signal to be projected has a wideband frequency characteristic. Here, high resolution sensing for inside of the target object may be further readily performed according to an increase in a bandwidth of a frequency. Also, the impulse method may project wideband signals at a time in an instant and thus, may quickly perform a sensing operation.
Also, the step frequency method refers to a method of sensing the inside of the target object by projecting a penetration signal several times through frequency modulation of, for example, a sine wave and thereby achieving the same effect as an effect achieved in the case of radiating a wideband signal. The step frequency method generates a wideband signal by dividing a modulation frequency of a sign wave into steps over time and thereby performing up-converting or down-converting, which is different from the impulse method of projecting wideband signals at a time in an instance. Therefore, a relatively large amount of time is used to generate a single wide band signal and thus, the step-frequency method may perform a sensing operation significantly slowly compared to the impulse method.
In the case of the impulse method, fast sensing may be performed, but a generated signal may have a poor frequency band characteristic. Further, generating high power impulse may be difficult. Accordingly, the impulse method is barely used to obtain a high resolution penetration signal.
In the case of the step frequency method, a generated signal may have an excellent frequency band characteristic and a signal may be generated with high power. Accordingly, the step frequency method may be advantageous in obtaining a high resolution penetration signal. However, as described above, the step frequency method may perform only slow sensing and thus, are restricted on a utilization and application field thereof.
A ground penetration radar technology may also be widely employed to verify a state of road traffic facilities, for example, to diagnose inside cracks of roads, to perform new routing, to measure the thickness of road pavement, and the like. Here, considering that an inside sensing depth of road traffic facilities needs to about 1 to 2 meters and sensing resolution needs to be within about 3 cm, the step frequency method among ground penetration radar technologies may be suitable.
However, in the case of performing a task using a ground penetration radar apparatus of a step frequency method, only slow sensing is possible and thus, an amount of work time may increase with the road traffic being controlled, thereby obstructing the traffic.